Electrochemical cell

ABSTRACT

An electrochemical cell includes a fuel electrode, an air electrode containing a perovskite type oxide as a main component, the perovskite type oxide being represented by a general formula ABO3 and containing La and Sr at the A site, and a solid electrolyte layer arranged between the fuel electrode and the air electrode. The air electrode includes a first portion and a second portion, the first portion being located on the most upstream side in a flow direction of an oxidant gas that flows through a surface of the air electrode, the second portion being located on the most downstream side in the flow direction. A first ratio of an La concentration to an Sr concentration detected at the first portion through Auger electron spectroscopy is at least 1.1 times a second ratio of an La concentration to an Sr concentration detected at the second portion through Auger electron spectroscopy.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of PCT/JP2020/000631, filed Jan. 10, 2020, whichclaims priority to Japanese Application No. 2019-014748, filed Jan. 30,2019, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to an electrochemical cell.

BACKGROUND ART

In recent years, fuel cells, which are one type of electrochemicalcells, are attracting attention from standpoint of environmentalproblems and effective utilization of energy resources. Fuel cellscommonly include a fuel electrode, an air electrode, and a solidelectrolyte layer that is arranged between the fuel electrode and theair electrode.

Perovskite type oxides, which are represented by a general formula ABO₃and contain La (lanthanum) and Sr (strontium) at an A site, arepreferable for the air electrode (see JP 2006-32132A, for example).

Examples of such perovskite type oxides include (La, Sr) (Co, Fe)O₃,(La, Sr)FeO₃, (La, Sr)CoO₃, and (La, Sr)MnO₃.

SUMMARY Technical Problem

However, output of a fuel cell may decrease as a result of powergeneration being repeated. Inventors of the present invention newlyfound that a reduction in the output is caused by deterioration of theair electrode, and one cause of the deterioration of the air electrodeis formation of a compound by La contained in the air electrode and B(boron). Note that B comes to the air electrode by flying from a memberlocated in a surrounding region, such as a support portion that supportsthe fuel cell.

An object of the present invention is to provide an electrochemical cellwith which a reduction in output can be suppressed.

Solution to Problem

An electrochemical cell according to the present invention includes afuel electrode, an air electrode containing a perovskite type oxide as amain component, the perovskite type oxide being represented by a generalformula ABO₃ and containing La and Sr at the A site, and a solidelectrolyte layer arranged between the fuel electrode and the airelectrode. The air electrode includes a first portion and a secondportion, the first portion being located on the most upstream side in aflow direction of an oxidant gas that flows through a surface of the airelectrode, the second portion being located on the most downstream sidein the flow direction. A first ratio of an La concentration to an Srconcentration detected at the first portion through Auger electronspectroscopy is at least 1.1 times a second ratio of an La concentrationto an Sr concentration detected at the second portion through Augerelectron spectroscopy.

Advantageous Effects

According to the present invention, it is possible to provide anelectrochemical cell with which a reduction in output can be suppressed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view showing a configuration of a fuel cellaccording to an embodiment.

DESCRIPTION OF EMBODIMENTS Configuration of Fuel Cell 100

A configuration of a fuel cell 100, which is one example of anelectrochemical cell according to the present embodiment, will bedescribed with reference to the accompanying drawing. FIG. 1 is aperspective view of the fuel cell 100.

The fuel cell 100 is a so-called solid oxide fuel cell (SOFC: SolidOxide Fuel Cell). The fuel cell 100 may be of various types such as aflat-tubular type, segmented-in-series type, a flat plate type, and acylindrical type.

The fuel cell 100 includes a fuel electrode 110, a solid electrolytelayer 120, and an air electrode 130. Although there is no particularlimitation on the shape of the fuel cell 100, the fuel cell 100 can havea square or rectangular plate shape having sides with a length of 10 to300 mm, for example.

In the fuel cell 100, power is generated based on the following chemicalreaction formulas (1) and (2) as a result of a fuel gas (e.g., hydrogen)being supplied to the fuel electrode 110 and an oxidant gas (e.g., air)being supplied to the air electrode 130.

(1/2).O₂+2e ⁻→O²⁻ (in the air electrode 130)  (1)

H₂+O²⁻→H₂O+2e ⁻ (in the fuel electrode 110)  (2)

The fuel electrode 110 is a porous body having good gas permeability.The fuel electrode 110 functions as an anode of the fuel cell 100. Thefuel electrode 110 is constituted by a substance that has electronconductivity and a substance that has oxygen ion conductivity. The fuelelectrode 110 can be constituted by NiO-8YSZ (yttria stabilizedzirconia) or NiO-GDC (gadolinium doped ceria), for example. Althoughthere is no particular limitation on the thickness of the fuel electrode110, the fuel electrode 110 can have a thickness of 50 to 2000 μm, forexample. Although there is no particular limitation on the porosity ofthe fuel electrode 110, the fuel electrode 110 can have a porosity of 15to 55%, for example.

The solid electrolyte layer 120 is arranged between the fuel electrode110 and the air electrode 130. The solid electrolyte layer 120 is acompact body through which oxygen ions generated in the air electrode130 can permeate. The solid electrolyte layer 120 functions as a sealfilm that prevents a fuel gas (e.g., hydrogen gas) from being mixed withan oxygen-containing gas (e.g., air).

The solid electrolyte layer 120 may contain ZrO₂ (zirconia) as a maincomponent. The solid electrolyte layer 120 may also contain additivessuch as Y₂O₃ (yttria) and/or Sc₂O₃ (scandium oxide), in addition tozirconia. These additives function as stabilizers. A molar compositionratio of stabilizers to zirconia (stabilizers:zirconia) in the solidelectrolyte layer 120 can be set to about 3:97 to 20:80. Accordingly,examples of materials of the solid electrolyte layer 120 include 3YSZ,8YSZ, 10 YSZ, and ScSZ (zirconia stabilized with scandia). The solidelectrolyte layer 120 can have a thickness of 3 μm to 50 μm, forexample. Although there is no particular limitation on the porosity ofthe solid electrolyte layer 120, the solid electrolyte layer 120 canhave a porosity of 0 to 10%, for example.

The air electrode 130 is a porous body having good gas permeability.There is no particular limitation on the plane shape (external shape ina plan view) of the air electrode 130, and the plane shape may be asquare, rectangular, circular, elliptical, or any other complex shape.

The air electrode 130 contains, as a main component, a perovskite typeoxide that is represented by a general formula ABO₃ and contains La(lanthanum) and Sr (strontium) at the A site. Examples of suchperovskite type oxides include, but are not limited to, (La, Sr) (Co,Fe)O₃ (lanthanum strontium cobalt ferrite), (La, Sr)FeO₃ (lanthanumstrontium ferrite), (La, Sr)CoO₃ (lanthanum strontium cobaltite), and(La, Sr)MnO₃ (lanthanum strontium manganate). Although there is noparticular limitation on the thickness of the air electrode 130, the airelectrode 130 can have a thickness of 50 to 2000 μm, for example.Although there is no particular limitation on the porosity of the airelectrode 130, the air electrode 130 can have a porosity of 15 to 55%,for example.

In the present embodiment, a substance Y “being contained as a maincomponent” in a composition X means that the substance Y constitutes atleast 70 weight % of the entire composition X.

As shown in FIG. 1, the air electrode 130 includes a first portion 130 aand a second portion 130 b.

Each of the first portion 130 a and the second portion 130 b extends ina plane direction that is perpendicular to a thickness direction of theair electrode 130. In a flow direction of an oxidant gas that flowsthrough a surface of the air electrode 130, the first portion 130 a islocated on an upstream side of the second portion 130 b. In the flowdirection, the second portion 130 b is located on a downstream side ofthe first portion 130 a. The second portion 130 b is a portion of theair electrode 130 other than the first portion 130 a. In the exampleshown in FIG. 1, each of the first portion 130 a and the second portion130 b has a rectangular plane shape, but the present invention is notlimited to this configuration. The first portion 130 a may also have anindeterminate plane shape, and the plane shape of the second portion 130b is determined according to the plane shape of the first portion 130 a.Although there is no particular limitation on a plane size of the firstportion 130 a, the first portion 130 a can have a plane size that is atleast 25% and smaller than 75% of the entire plane area of the airelectrode 130. Although there is no particular limitation on a planesize of the second portion 130 b, the second portion 130 b can have aplane size that is at least 25% and smaller than 75% of the entire planearea of the air electrode 130. Note that the thickness direction of theair electrode 130 is the same as a direction in which the fuel electrode110, the solid electrolyte layer 120, and the air electrode 130 arelayered.

The first portion 130 a and the second portion 130 b may also be formedas a single piece. That is, the first portion 130 a and the secondportion 130 b need not have a clear boundary therebetween.

La/Sr Ratio at Air Electrode 130

A first ratio (La concentration/Sr concentration) Qa of a quantitativevalue of La (hereinafter referred to as an “La concentration”) to aquantitative value of Sr (hereinafter referred to as an “Srconcentration”) detected at the first portion 130 a through Augerelectron spectroscopy is at least 1.1 times a second ratio (Laconcentration/Sr concentration) Qb of an La concentration to an Srconcentration detected at the second portion 130 b through Augerelectron spectroscopy. That is, Qa≥1.1×Qb.

With this configuration, a composition ratio of La at the first portion130 a can be made sufficiently higher than a composition ratio of La atthe second portion 130 b to cause B (boron) to preferentially react withLa contained in the first portion 130 a during electric conduction. As aresult of B being trapped by La contained in the first portion 130 a asdescribed above, B can be kept from reacting with La in the secondportion 130 b and forming a compound. Accordingly, a reduction incatalyst reaction activity at the second portion 130 b can besuppressed, and deterioration of the air electrode 130 as a whole can besuppressed. As a result, a reduction in output of the fuel cell 100 canbe suppressed.

The first ratio Qa at the first portion 130 a is preferably not largerthan 1.6 times the second ratio Qb at the second portion 130 b. Thisconfiguration can reduce a difference in reaction activity between thefirst portion 130 a and the second portion 130 b during electricconduction, and accordingly can suppress local deterioration of the airelectrode 130 due to generation of a current density distribution. Thefirst ratio Qa at the first portion 130 a is more preferably not largerthan 1.3 times the second ratio Qb at the second portion 130 b.

Although there is no particular limitation on a numerical value range ofthe first ratio Qa at the first portion 130 a, the first ratio Qa ispreferably at least 0.3 and not larger than 0.55, for example. Althoughthere is no particular limitation on a numerical value range of thesecond ratio Qb at the second portion 130 b, the second ratio Qb ispreferably at least 0.25 and not larger than 0.4, for example. With thisconfiguration, deterioration of the air electrode 130 can be furthersuppressed.

The following describes a method for determining the first ratio Qa atthe first portion 130 a and the second ratio Qb at the second portion130 b.

First, in a plan view of the air electrode 130, four first measurementpoints for calculating the first ratio Qa are arbitrarily selected frompositions located at a distance of ¼ of the entire length of the airelectrode 130 in the flow direction from an upstream end of the airelectrode 130. Also, in the plan view of the air electrode 130, foursecond measurement points for calculating the second ratio Qb arearbitrarily selected from positions located at a distance of ¾ of theentire length of the air electrode 130 in the flow direction from theupstream end of the air electrode 130.

Next, La intensity data and Sr intensity data are obtained for each ofthe four first measurement points using a scanning Auger electronspectroscopy apparatus (manufactured by ULVAC-PHI, Inc., Model-710,electron beam acceleration voltage: 10 kV). Next, an La concentration isdetermined for each first measurement point by dividing the La intensitydata by an La relative sensitivity factor, and an Sr concentration isdetermined for each first measurement point by dividing the Sr intensitydata by an Sr relative sensitivity factor. Next, a mean La concentrationis determined by calculating an arithmetic mean of the La concentrationsof the four first measurement points, and a mean Sr concentration isdetermined by calculating an arithmetic mean of the Sr concentrations ofthe four first measurement points. Then, a value obtained by dividingthe mean La concentration by the mean Sr concentration is taken to bethe first ratio Qa.

Similarly, La intensity data and Sr intensity data are obtained for eachof the four second measurement points using the scanning Auger electronspectroscopy apparatus (manufactured by ULVAC-PHI, Inc., Model-710,electron beam acceleration voltage: 10 kV). Next, an La concentration isdetermined for each second measurement point by dividing the Laintensity data by the La relative sensitivity factor, and an Srconcentration is determined for each second measurement point bydividing the Sr intensity data by the Sr relative sensitivity factor.Next, a mean La concentration is determined by calculating an arithmeticmean of the La concentrations of the four second measurement points, anda mean Sr concentration is determined by calculating an arithmetic meanof the Sr concentrations of the four second measurement points. Then, avalue obtained by dividing the mean La concentration by the mean Srconcentration is taken to be the second ratio Qb.

Note that the La relative sensitivity factor and the Sr relativesensitivity factor are determined according to the electron beamacceleration voltage of the scanning Auger electron spectroscopyapparatus. If the electron beam acceleration voltage is 10 kV, the Larelative sensitivity factor is 0.652 and the Sr relative sensitivityfactor is 0.059.

Method for Manufacturing Fuel Cell 100

A method for manufacturing the fuel cell 100 will be described.

First, a slurry is prepared by mixing a mixed powder (e.g., a mixture ofan NiO powder and an YSZ powder) for forming the fuel electrode 110 withan organic binder and a solvent. Then, a fuel electrode sheet (a compactfor the fuel electrode 110) is formed using the slurry.

Next, a slurry is prepared by mixing a powder (e.g., an YSZ powder) forforming the solid electrolyte layer 120 with water and a binder. Then, asolid electrolyte layer sheet (a compact for the solid electrolyte layer120) is formed by applying the slurry to the compact for the fuelelectrode 110.

Next, thermal treatment is performed on the compacts for the fuelelectrode 110 and the solid electrolyte layer 120 to remove the binders,and then the compacts are fired together at 1300 to 1600° C. in anoxygen-containing atmosphere to obtain a co-fired body of the fuelelectrode 110 and the solid electrolyte layer 120.

Next, powders (perovskite type oxide powders represented by a generalformula ABO₃ and containing La and Sr at the A site) for forming thecenter portion 130 a and the outer peripheral portion 130 b of the airelectrode 130 are prepared. A perovskite type oxide powder that has alarger composition ratio (La/Sr) of La to Sr than the perovskite typeoxide powder for forming the center portion 130 a is used as theperovskite type oxide powder for forming the outer peripheral portion130 b.

Next, a compact for the first portion 130 a is formed by dipping anapplication liquid, which is obtained by dispersing a first portionmaterial for forming the first portion 130 a in a solvent, on a surfaceof the solid electrolyte layer 120.

Next, a compact for the second portion 130 b is formed by dipping anapplication liquid, which is obtained by dispersing a second portionmaterial for forming the second portion 130 b in a solvent, to a regionadjacent to the compact for the first portion 130 a.

Next, the compact for the air electrode 130 is fired at 1000 to 1300° C.to form the air electrode 130.

Variations

The embodiment of the present invention has been described, but thepresent invention is not limited to this embodiment and variousalterations can be made without departing from the gist of the presentinvention.

In the above-described embodiment, the fuel cell 100 is described as oneexample of the electrochemical cell, but the present invention can alsobe applied to electrochemical cells such as solid oxide electrolysiscells, as well as fuel cells.

In the above-described embodiment, the fuel cell 100 includes the fuelelectrode 110, the solid electrolyte layer 120, and the air electrode130, but the present invention is not limited to this configuration. Forexample, the fuel cell 100 may also include a barrier layer forsuppressing formation of a high resistivity layer between the solidelectrolyte layer 120 and the air electrode 130. The barrier layer canbe formed using a ceria-based material including ceria and a solidsolution of ceria and a rare earth metal oxide, for example. Examples ofsuch ceria-based materials include GDC (gadolinium doped ceria) and SDC(samarium doped ceria).

EXAMPLES

The following describes examples of fuel cells according to the presentinvention, but the present invention is not limited to the followingexamples.

Production of Samples No. 1 to No. 10

Fuel cells according to samples No. 1 to No. 10 were produced asdescribed below.

First, a slurry that was obtained by mixing a blended powder of an NiOpowder, a Y₂O₃ powder, and a pore forming material (PMMA) with IPA wasdried in a nitrogen atmosphere to prepare a mixed powder.

Next, the mixed powder was pressed using a uniaxial press (compactingpressure: 50 MPa) to form a plate having a length of 30 mm, a width of30 mm, and a thickness of 3 mm, and the plate was further consolidatedusing a CIP (compacting pressure: 100 MPa) to form a compact for a fuelelectrode power collection layer.

Next, a slurry that was obtained by mixing a blended powder of NiO-8YSZand PMMA with IPA was applied to the compact for the fuel electrodepower collection layer to form a compact for a fuel electrode activelayer. Thus, a compact for the fuel electrode was obtained.

Next, a slurry for the solid electrolyte layer was prepared by mixing8YSZ with terpineol and a binder. Then, the slurry for the solidelectrolyte layer was applied to the compact for the fuel electrode toform a compact for the solid electrolyte layer.

Next, a GDC slurry was prepared and applied to the compact for the solidelectrolyte layer to form a compact for a barrier layer.

Next, the compacts for the fuel electrode, the solid electrolyte layer,and the barrier layer were fired (at 1450° C. for 5 hours) to form alayered body constituted by the fuel electrode, the solid electrolytelayer, and the barrier layer.

Next, a first portion slurry was prepared by mixing a first portionmaterial shown in Table 1 with terpineol and a binder. Also, a secondportion slurry was prepared by mixing a second portion material shown inTable 1 with terpineol and a binder. As shown in Table 1, a materialthat had a larger composition ratio (La/Sr) of La to Sr than the secondportion material was used as the first portion material.

Next, the first portion slurry and the second portion slurry wereapplied to the barrier layer in that order from the upstream side in theflow direction of the oxidant gas to form a compact for the airelectrode.

Next, the compact for the air electrode was fired (at 1000° C. for 1hour) to form the air electrode. In the flow direction, the firstportion and the second portion had the same width. La/Sr Ratio at FirstPortion and Second Portion of Air Electrode

First, in a plan view of the air electrode, four first measurementpoints for calculating the first ratio Qa were arbitrarily selected frompositions located at a distance of ¼ of the entire length of the airelectrode in the flow direction from the upstream end of the airelectrode. Also, in the plan view of the air electrode, four secondmeasurement points for calculating the second ratio Qb were arbitrarilyselected from positions located at a distance of ¾ of the entire lengthof the air electrode in the flow direction from the upstream end of theair electrode.

Next, La intensity data and Sr intensity data were obtained for each ofthe four first measurement points using a scanning Auger electronspectroscopy apparatus (manufactured by ULVAC-PHI, Inc., Model-710,electron beam acceleration voltage: 10 kV). Next, an La concentrationwas determined for each first measurement point by dividing the Laintensity data by an La relative sensitivity factor (=0.652), and an Srconcentration was determined for each first measurement point bydividing the Sr intensity data by an Sr relative sensitivity factor(=0.059). Next, a mean La concentration was determined by calculating anarithmetic mean of the La concentrations of the four first measurementpoints, and a mean Sr concentration was determined by calculating anarithmetic mean of the Sr concentrations of the four first measurementpoints. Then, the first ratio Qa was determined by dividing the mean Laconcentration by the mean Sr concentration.

Similarly, La intensity data and Sr intensity data were obtained foreach of the four second measurement points using the scanning Augerelectron spectroscopy apparatus (manufactured by ULVAC-PHI, Inc.,Model-710, electron beam acceleration voltage: 10 kV). Next, an Laconcentration was determined for each second measurement point bydividing the La intensity data by the La relative sensitivity factor(=0.652), and an Sr concentration was determined for each secondmeasurement point by dividing the Sr intensity data by the Sr relativesensitivity factor (=0.059). Next, a mean La concentration wasdetermined by calculating an arithmetic mean of the La concentrations ofthe four second measurement points, and a mean Sr concentration wasdetermined by calculating an arithmetic mean of the Sr concentrations ofthe four second measurement points. Then, the second ratio Qb wasdetermined by dividing the mean La concentration by the mean Srconcentration.

Table 1 shows the first ratio Qa, the second ratio Qb, and the ratio ofthe first ratio Qa to the second ratio Qb.

Durability Test

Each of the samples from No. 1 to No. 10 was heated to 750° C. whilesupplying a nitrogen gas to the fuel electrode side and supplying air tothe air electrode side, and once the temperature reached 750° C.,reduction treatment was performed for 3 hours while supplying a hydrogengas to the fuel electrode.

Thereafter, a voltage drop rate per 1000 hours was measured as adeterioration rate. A value obtained at a temperature of 750° C. and arated current density of 0.2 A/cm² was used. Table 1 shows measurementresults. In Table 1, samples having a deterioration rate lower than 1.0%are evaluated as “excellent”, samples having a deterioration rate of atleast 1.0% and lower than 1.1% are evaluated as “good”, samples having adeterioration rate of at least 1.1% and lower than 1.2% are evaluated as“fair”, and samples having a deterioration rate of at least 1.2% areevaluated as “poor”.

TABLE 1 First Second Material for first portion Material for secondportion ratio Qa ratio Qb Sample on upstream side in flow on downstreamside in flow at first at second Deterioration No. direction of oxidantgas direction of oxidant gas portion portion Qa/Qb rate (%) Evaluation 1(La₆,Sr₄)(Co₂,Fe₈)O₃ (La₆,Sr₄)(Co₂,Fe₈)O₃ 0.3 0.3 1.0 1.3 Poor 2(La_(6.2),Sr_(3.8))(Co₂,Fe₈)O₃ (La₆,Sr₄)(Co₂,Fe₈)O₃ 0.33 0.3 1.1 0.9Excellent 3 (La_(7.2),Sr_(2.8))(Co₂,Fe₈)O₃(La_(6.7),Sr_(3.3))(Co₂,Fe₈)O₃ 0.5 0.4 1.3 0.75 Excellent 4(La_(6.7),Sr_(3.3))(Co₂,Fe₈)O₃ (La_(5.5),Sr_(4.5))(Co₂,Fe₈)O₃ 0.4 0.251.6 1.08 Good 5 (La_(7.4),Sr_(2.6))(Co₂,Fe₈)O₃(La_(6.7),Sr_(3.3))(Co₂,Fe₈)O₃ 0.55 0.4 1.4 1.0 Good 6(La_(7.2),Sr_(2.8))(Co₂,Fe₈)O₃ (La₆,Sr₄)(Co₂,Fe₈)O₃ 0.5 0.3 1.7 1.1 Fair7 (La_(6.2),Sr_(3.8))FeO₃ (La_(6.2),Sr_(3.8))FeO₃ 0.33 0.33 1.0 1.3 Poor8 (La_(6.5),Sr_(3.5))FeO₃ (La_(6.2),Sr_(3.8))FeO₃ 0.36 0.33 1.1 0.85Excellent 9 (La_(7.2),Sr_(2.8))FeO₃ (La_(6.7),Sr_(3.3))FeO₃ 0.5 0.4 1.30.8 Excellent 10 (La_(7.4),Sr_(2.6))FeO₃ (La₆,Sr₄)FeO₃ 0.55 0.3 1.8 1.15Fair

As shown in Table 1, the deterioration rate of the air electrode couldbe reduced in samples in which the first ratio Qa at the first portionwas at least 1.1 times the second ratio Qb at the second portion. Thisis because a reduction in catalyst reaction activity at the secondportion could be suppressed as a result of B (boron) being trapped by Lacontained in the first portion.

Also, among the samples in which the first ratio Qa at the first portionwas at least 1.1 times the second ratio Qb at the second portion, insamples in which the first ratio Qa was not larger than 1.6 times thesecond ratio Qb, the deterioration rate of the air electrode could befurther suppressed. This is because generation of a current densitydistribution due to a difference in reaction activity between the firstportion and the second portion could be suppressed during electricconduction, and accordingly local deterioration of the air electrodecould be suppressed.

Furthermore, among the samples in which the first ratio Qa at the firstportion was at least 1.1 times the second ratio Qb at the secondportion, in samples in which the first ratio Qa was not larger than 1.3times the second ratio Qb, the deterioration rate of the air electrodecould be further suppressed.

Note that although SrSO₄, Co₃O₄, CoO, SrO, and the like are known assubstances that may cause deterioration of the air electrode, it wasconfirmed through experiments that the above-described effects can beachieved even if the air electrode contains these substances.

1. An electrochemical cell comprising: a fuel electrode; an airelectrode containing a perovskite type oxide as a main component, theperovskite type oxide being represented by a general formula ABO₃ andcontaining La and Sr at the A site; and a solid electrolyte layerarranged between the fuel electrode and the air electrode, wherein theair electrode includes a first portion and a second portion, the firstportion being located on the most upstream side in a flow direction ofan oxidant gas that flows through a surface of the air electrode, thesecond portion being located on the most downstream side in the flowdirection, and a first ratio of an La concentration to an Srconcentration detected at the first portion through Auger electronspectroscopy is at least 1.1 times a second ratio of an La concentrationto an Sr concentration detected at the second portion through Augerelectron spectroscopy.
 2. The electrochemical cell according to claim 1,wherein the first ratio is not larger than 1.6 times the second ratio.3. The electrochemical cell according to claim 1, wherein the firstratio is not larger than 1.3 times the second ratio.